The present invention relates to a multi layered member, more particularly to a resilient such multi layered member, and to a method of manufacture thereof, and particularly may be applied to an automotive interior member such as a door trim, a padded instrument panel, or the like. Even more particularly, the present invention relates to such a resilient multi layered member, which particularly incorporates a cushion layer for the purpose of improving its various characteristics such as its external appearance, its feel to the user, and its thickness and durability, and to a method of manufacture thereof.
In the prior art, there have been proposed various types of resilient multi layered members, such as are utilized in automotive applications as door trims, padded instrument panels, and the like. Such resilient multi layered members are required to have a favorable external appearance and feel, as well as having uniform thickness which does not change over time. Such resilient multi layered members have typically been formed by the so called slush molding process. Particularly, in Japanese Patent Laying Open Publication Ser. No. 58-32720 (1983), which it is not hereby intended to admit as prior art to the present patent application except to the extent in any case mandated by applicable law, there are disclosed a resilient multi layered member and a method for making it, which will now be explained with regard to FIG. 5 of the appended drawings, which is a pair of transverse cross sectional views showing such a slush molding process.
Referring to FIG. 5 first a layer of non foaming sol material is laid onto and adhered onto the internal surface of a metallic mold 1, which is formed in the desired external shape of the member which is to manufactured--this metallic mold 1 will be termed the outer mold henceforward in this specification. This may be done by layering PVC (polyvinyl chloride) powder against the internal surface of said outer mold 1, for example. This layer of non foaming sol material is then made into a gel, for example by heating it up, so as to form a surface skin layer 2 over the internal surface of the outer mold 1. Then a plastic sol material is mixed with a foaming agent and is laid as a gel over the upper surface of this surface skin layer 2 as it lies in the outer mold 1, so as to form a foam layer 3. And then, while this foam layer 3 is still soft, a core layer 4, which is relatively stiff and typically may be made in advance from a molded resin material or a composite molded resin material by a per se known process, and which is formed into a shape complementary to the shape of the outer mold 1, is set onto and against the foam layer 3, so that said foam layer 3 and said core layer 4 join together into an integral body. The whole layered mass then is allowed to cool, and then is removed from the outer mold 1 to constitute a multi layered member, which is resilient due to the presence of the foam layer 3 between the surface skin layer 2 and the core layer 4. This resilient multi layered member may be used as an automotive interior member such as a door trim panel or a dash board panel, for example.
However, this process is subject to a number of problems.
First, it is difficult to form evenly the layer of PVC resin powder on the internal surface of the outer mold 1 in order to form the surface skin layer 2, because the temperature distribution on said internal surface of said outer mold 1 may well be rather uneven.
Second, it is difficult to control adequately the thickness of the foam layer 3, and it is likely that pockets of air will be included between said foam layer 3 and the core layer 4 which is adhered thereagainst. Such pockets of air are schematically shown in the lower portion of FIG. 5.
Third, since the core layer 4 is necessarily placed over the foam layer 3 while said foam layer 3 is still soft in order to secure good adhesion of said core layer 4 to said foam layer 3, certain quantities of gas are necessarily still being evolved from said foam layer 3 due to the chemical foaming reaction therein which is still proceeding to a certain extent, and these quantities of gas are responsible for the generation of gas pockets between said foam layer 3 and said core layer 4, also schematically shown in the lower portion of FIG. 5.
For all these reasons, it is hard to maintain a constant thickness for the finished products. Further, the irregular pockets of air and gas between the foam layer 3 and the core layer 4 tends to produce irregularities in the surface of the surface skin layer 2, which deteriorates the appearance of the finished products. And, further, the feel of said finished products when touched by a user thereof is rendered uneven and disagreeable by the presence of said irregular pockets of air and gas. And the possible collapse, during use of the resilient multi layered member, of such irregular pockets of air and gas, can cause the thickness of the resilient multi layered member to vary after its manufacture and during its period of use.